Engine exhaust gases may be treated by a catalyst to purify the exhaust emissions by chemical reaction as the exhaust gases flow through the catalyst. As an example, a catalytic converter containing a catalyst may be located at the exhaust pipe, such that the catalyst helps convert carbon monoxide in the exhaust into carbon dioxide. Other reactions may also take place, such as converting hydrocarbons into carbon dioxide and water, and converting nitrogen oxides back into nitrogen and oxygen.
Typically such exhaust gas treatment systems require knowledge of the temperature of the exhaust gas. Further, since the chemical reactions in the catalyst may be exothermic, such that heat is released into exhaust, previous solutions of exhaust gas temperature estimation models include modeling of the additional heat due to the catalytic exotherm.
The inventors of the present application have recognized a problem in such previous solutions, in that such models assume perfect mixing and burning of the complete air and fuel inside the cylinder. However, in the event that air escapes from the intake to the exhaust without getting trapped inside the cylinder (e.g., blowthrough air), this blowthrough air may oxidize any unburned constituents in the exhaust gas in the presence of the catalyst. Such reactions may be exothermic, such that the reactions release heat into the exhaust gases, thereby increasing the catalyst temperature. In some cases, such blowthrough may occur as part of a blowthrough mode (e.g., in turbo applications). By not accounting for this additional heat, typical calculations underestimate the exhaust temperature, which may lead to damage of catalyst materials due to overheating. For these reasons, the inventors of the present application have included the effect of blowthrough air on exhaust gas temperature, and then provided various approaches for advantageously using the improved catalyst temperature estimate.
In one example, some of the above issues may be addressed by a method of calculating a temperature of exhaust from an engine, wherein the method comprises determining a temperature of the exhaust, determining a catalyst exotherm based on an amount of blowthrough air and a combustion air-fuel ratio, and adjusting the determined temperature of the exhaust based on the determined catalyst exotherm. The determined temperature may include a catalyst temperature, such as a catalyst mid-bed temperature. Additionally, the temperatures may be determined taking into account the amount of exotherm occurring in the exhaust port and/or manifold, versus the amount of exotherm occurring in the catalyst. Further, various parameters may be adjusted based on the exhaust (e.g., catalyst) temperature, such as engine air-fuel ratio, engine airflow, and/or others to compensate for the increased temperature and/or to abate the increased temperature.
In this way, it is possible to obtain accurate exhaust and/or catalyst temperatures, even during conditions generating blowthrough, such as boosted intake-exhaust valve overlap conditions with rich combustion in the engine cylinder. For example, in the case of an overall stoichiometric exhaust air-fuel mixture, the engine may be fueled for rich combustion during a boosting operation. Thus, excess fresh air that blows through the cylinder mixes the rich combustion gases to form an overall stoichiometric air-fuel ratio. In such a case, the rich air-fuel mixture in the cylinder may produce higher levels of CO, which then combine with oxygen from blowthrough air in an exothermic reaction releasing heat into the exhaust and thus increasing the temperature of the exhaust. However, depending on the exhaust port temperatures, more or less of the exotherm may occur in the exhaust port (and a corresponding less or greater amount may occur in the catalyst). Accordingly, modeling the catalyst exotherm due to blowthrough air, and taking into account whether more or less of the oxidation occurs in the catalyst or elsewhere, allows for a more accurate estimation of exhaust temperature.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.